21005455 has 16 divisors (see below), whose sum is σ = 27414720. Its totient is φ = 15386112.

The previous prime is 21005441. The next prime is 21005473. The reversal of 21005455 is 55450012.

It is a cyclic number.

It is not a de Polignac number, because 21005455 - 2⁵ = 21005423 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 195 + ... + 6484.

It is an arithmetic number, because the mean of its divisors is an integer number (1713420).

Almost surely, 2^21005455 is an apocalyptic number.

21005455 is a deficient number, since it is larger than the sum of its proper divisors (6409265).

21005455 is a wasteful number, since it uses less digits than its factorization.

21005455 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6738.

The product of its (nonzero) digits is 1000, while the sum is 22.

The square root of 21005455 is about 4583.1708456046. The cubic root of 21005455 is about 275.9163043499.

Adding to 21005455 its reverse (55450012), we get a palindrome (76455467).

The spelling of 21005455 in words is "twenty-one million, five thousand, four hundred fifty-five".